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authorLawrence Brakmo <brakmo@fb.com>2018-01-25 16:14:08 -0800
committerAlexei Starovoitov <ast@kernel.org>2018-01-25 16:41:14 -0800
commitb73042b8a28e2603ac178295ab96c876ba5a97a1 (patch)
treec3db00b9c7a9b9816bb3392f9fa59f7d8b4a5e49 /net
parent34d367c59233464dbd1f07445c4665099a7128ec (diff)
bpf: Add write access to tcp_sock and sock fields
This patch adds a macro, SOCK_OPS_SET_FIELD, for writing to struct tcp_sock or struct sock fields. This required adding a new field "temp" to struct bpf_sock_ops_kern for temporary storage that is used by sock_ops_convert_ctx_access. It is used to store and recover the contents of a register, so the register can be used to store the address of the sk. Since we cannot overwrite the dst_reg because it contains the pointer to ctx, nor the src_reg since it contains the value we want to store, we need an extra register to contain the address of the sk. Also adds the macro SOCK_OPS_GET_OR_SET_FIELD that calls one of the GET or SET macros depending on the value of the TYPE field. Signed-off-by: Lawrence Brakmo <brakmo@fb.com> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'net')
-rw-r--r--net/core/filter.c48
1 files changed, 48 insertions, 0 deletions
diff --git a/net/core/filter.c b/net/core/filter.c
index dbb6d2f60680..c356ec02b1a5 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4491,6 +4491,54 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
offsetof(OBJ, OBJ_FIELD)); \
} while (0)
+/* Helper macro for adding write access to tcp_sock or sock fields.
+ * The macro is called with two registers, dst_reg which contains a pointer
+ * to ctx (context) and src_reg which contains the value that should be
+ * stored. However, we need an additional register since we cannot overwrite
+ * dst_reg because it may be used later in the program.
+ * Instead we "borrow" one of the other register. We first save its value
+ * into a new (temp) field in bpf_sock_ops_kern, use it, and then restore
+ * it at the end of the macro.
+ */
+#define SOCK_OPS_SET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ) \
+ do { \
+ int reg = BPF_REG_9; \
+ BUILD_BUG_ON(FIELD_SIZEOF(OBJ, OBJ_FIELD) > \
+ FIELD_SIZEOF(struct bpf_sock_ops, BPF_FIELD)); \
+ if (si->dst_reg == reg || si->src_reg == reg) \
+ reg--; \
+ if (si->dst_reg == reg || si->src_reg == reg) \
+ reg--; \
+ *insn++ = BPF_STX_MEM(BPF_DW, si->dst_reg, reg, \
+ offsetof(struct bpf_sock_ops_kern, \
+ temp)); \
+ *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF( \
+ struct bpf_sock_ops_kern, \
+ is_fullsock), \
+ reg, si->dst_reg, \
+ offsetof(struct bpf_sock_ops_kern, \
+ is_fullsock)); \
+ *insn++ = BPF_JMP_IMM(BPF_JEQ, reg, 0, 2); \
+ *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF( \
+ struct bpf_sock_ops_kern, sk),\
+ reg, si->dst_reg, \
+ offsetof(struct bpf_sock_ops_kern, sk));\
+ *insn++ = BPF_STX_MEM(BPF_FIELD_SIZEOF(OBJ, OBJ_FIELD), \
+ reg, si->src_reg, \
+ offsetof(OBJ, OBJ_FIELD)); \
+ *insn++ = BPF_LDX_MEM(BPF_DW, reg, si->dst_reg, \
+ offsetof(struct bpf_sock_ops_kern, \
+ temp)); \
+ } while (0)
+
+#define SOCK_OPS_GET_OR_SET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ, TYPE) \
+ do { \
+ if (TYPE == BPF_WRITE) \
+ SOCK_OPS_SET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ); \
+ else \
+ SOCK_OPS_GET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ); \
+ } while (0)
+
case offsetof(struct bpf_sock_ops, snd_cwnd):
SOCK_OPS_GET_FIELD(snd_cwnd, snd_cwnd, struct tcp_sock);
break;